The invention relates to an air filter for an internal combustion engine.
In internal combustion engines for motor vehicles the raw air inlet is usually arranged in an area into which cold air can enter unhampered. The air inlet is therefore normally situated behind the radiator grille of the vehicle or in the area of a fender. It has been found that, in especially cold countries, when travel is encumbered by heavy snowfall and swirling snow, snow is drawn in with the raw air, and this snow is deposited on the filter insert and, under certain circumstances, clogs the filter insert. This causes the motor to stall.
It is furthermore disadvantageous that, when the motor is turned off, the snow on the air filter insert thaws and forms an ice coating which prevents the entry of air into the motor and thus interferes with the starting of the motor.
It is therefore proposed in G 93 07 147.7 to provide an air filter for an internal combustion engine in which the raw air inlet is provided with a sieve. Furthermore, a second raw air inlet is provided, which has a flap valve, this valve opening depending on the vacuum prevailing in the filter housing. This signifies that the penetration of snow is hampered by the sieve and xe2x80x94in case the sieve is plugged with snowxe2x80x94the second flap opens and thus snow-free raw air can be drawn in. The sieve thus effectively prevents the penetration of snow. Of course, this has the consequence of a loss of performance, since a certain portion of the raw air inlet has its cross section reduced by the sieve structure. It was therefore attempted to increase the mesh width of the sieve. However, this enables flying snow to penetrate and the disadvantages described above occur, such as the clogging of the filter insert.
Of course, it is also possible to make the raw air inlet cross section larger. Even this entails disadvantages, including among other things, the result that more intake air noise is generated.
It is therefore the object of the invention to provide an air filter for an internal combustion engine, which will assure optimum separation of snow and also will not reduce the cross-sectional area of the raw air inlet to any substantial extent, if at all.
This object is achieved.
The advantage of the invention is that the sieve closing the raw air inlet or the closed flap opens or closes depending on the raw air temperature. The performance of the movement can be controlled, for example, by a wax thermostat. Thus, at a temperature above a certain value, the full cross section of the raw air opening remains available. The internal combustion engine can develop its maximum power. Below the temperature limit, i.e., for example at a temperature of less than +2xc2x0 C., the sieve or the flap closes the raw air inlet and thus prevents entry of snow.
In accordance with one embodiment of the invention, the additional raw air inlet is provided with a weight-loaded or spring-loaded flap. The closing force is established such that the valve opens only at a vacuum which is formed when the sieve is clogged with snow or the flap has closed due to the temperature of the raw air opening.
An additional embodiment of the invention provides for arranging the additional raw air inlet in the area of a snow-free zone of the motor compartment. For example, this can be in back of the air cooler. It is also possible to arrange this raw air inlet near the exhaust manifold, in order thereby to take in heated air.
In order to open the raw air inlet provided with the sieve or the flap, different actuating means can be provided. It is possible to sense the vacuum in the raw air part of the air filter and generate a control signal which activates an actuator in accordance with the sensed vacuum. It is also possible to provide a simple expansion thermostat which at a certain temperature turns the sieve or the flap to the appropriate position. Additional possibilities for turning the sieve or flap are magnetic drivers or electric drivers.
These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, the individual features being applicable individually or severally in the form of subcombinations in the embodiment of the invention and in other fields and may represent advantageous as well as independently patentable embodiments, for which protection is hereby claimed.